Various types of brushless d-c motors and energization circuits have been proposed in which the stator winding is formed of a continuous group of series connection winding sections or portions distributed about the circumference of the stator, and connected in a closed ring, with junction points at the connection of the respective windings. The rotor may be a permanent magnet rotor, in which the motor then will be truly "brushless"; or it may be an electromagnetically excited rotor having slip rings to supply field energy thereto. The referenced publication "ATM" of April 1968, pp. 79-82, article by Gerhard Kruger "Kollektorlose Gleichstrommotoren" ("Brushless D-C Motors") describes a brushless d-c motor in which the windings are stationary, secured to the stator, and the magnetic flux is generated by a permanent magnet forming the rotor. In known d-c motors of this type, current is switched to respective winding sections of the stator by transistors forming contactless switches which are controlled between conductive and non-conductive state by Hall generators. The Hall generators are located in the magnetic field of the rotor. The current can be switched and reversed under control of the transistors. Known circuits of this type are complex and, in order to reduce the circuit component requirements, the windings can be connected, not in series, but rather in a star or common center connection to be sequentially connected to a current source in dependence on the relative position of the rotor with respect to the winding sections. Such motors function satisfactorily; however, the output torque is undulating and variable.
Electronic commutating systems have previously been proposed--see U.S. Pat. No. 3,619,746--for use with a d-c motor having an even number of stationary windings in the stator connected in ring connection. The rotor field is generated either by a permanent magnet or by an electromagnet receiving energy over slip rings. Hereinafter, the invention will be described in connection with a "brushless" motor in the sense that there are no brushes selectively contacting commutator segments; brushes which supply current to slip rings are not here considered, so that the term "brushless" motor is deemed to include also excited field motors.
U.S. Pat. No. 3,619,746 also describes a circuit to energize the respective windings by connecting to junctions of serially connected winding sections a pair of transistors which, in dependence on an external clock source, or signals from a rotor position detector are respectively controlled to conduction, so that on each two diametrically oppositely located junctions one terminal or the other of a power source are connected. The circuit requirements to ignite and extinguish the thyristors, that is, to control them to conduction and then to interrupt their conduction, is considerable. Additionally, voltage separation between the control circuit and the supply circuit must be observed, so that the overall circuit requirements are increased further thereby.